An antifoulant for petrochemical processes

Abstract: An antifoulant for petrochemical processes comprising a hydrogen-donating hydroaromatic compound is disclosed. It can be handled easily, is inexpensive, has no adverse effect on the process, shows excellent effect to prevent formation of fouling, and enables continuous operation of a plant for a long time with good stability.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel antifoulant for petrochemical processes. More particularly, it relates to an antifoulant for petrochemical processes which can effectively prevent formation of fouling in processes in a petrochemical plant, such as the rectification process in an ethylene plant. 2. Description of the Related Art In a petrochemical plant, such as an ethylene plant, distillation of a fluid containing olefins, such as ethylene and propylene, and diolefins, such as butadiene, has been conducted. In a process of distillation of such a fluid, it is inevitable that the fluid is modified with heat to form sludge by heating, for example, in a preliminary heat exchanger or a reboiler and the sludge thus formed is adhered to the surface of heat transfer in the preliminary heat exchanger or the reboiler or to the surface of pipings to form fouling. As the mechanism of the formation of fouling, the following phenomena are known. In petrochemical processes, organic compounds which are easily oxidized, such as unsaturated hydrocarbons like olefins and diolefins, in process fluids are led to hydroperoxides by the dissolved oxygen. The hydroperoxides are then decomposed with heat, particularly in the presence of a substance having a catalytic activity, such as a metal, to form ketones, aldehydes, carboxylic acids and the like. These compounds are polymerized to form sludge of oligomers and polymers. Therefore, antioxidants, such as phenolic antioxidants and amine antioxidants, polymerization inhibitors, such as oxime inhibitors and nitroso inhibitors, dispersants to prevent formation of sludge and adherence of deposit, and agents in combinations of these agents, have heretofore been used in petrochemical processes as antifoulants for the purpose of preventing fouling described above. For examples, (1) an antifoulant comprising a combination of aniline and t-butylcatechol (Japanese Patent Publication Showa 59(1984)-24138, (2) an antifoulant comprising nitrosophenol (Japanese Patent Application Laid-Open No. Heisei 3(1991)-350147, (3) an antifoulant comprising a nitroso compound (Japanese Patent Publication Heisei 4(1992)-26639, and (4) an antifoulant comprising an amine compound (Japanese Patent Application Laid-Open No. Showa 64(1989)-13041, have been disclosed. However, because these antifoulants are added directly to a process, they have drawbacks that coloring of the product is caused, that unfavorable by-products are formed, and, moreover, that they are not easy to handle, are expensive and have insufficient effect of preventing fouling to cause problems in a continuous operation for a long time, such as for two years or longer. As described above, conventional antifoulants are not always satisfactory. Thus, development of an antifoulant for petrochemical processes which can be handled easily, is inexpensive, has no adverse effect on the process, shows excellent effect to prevent the formation of fouling, and enables continuous operation for a long time with good stability, has strongly been desired. WO-A-9117230 describes the use of HDD compounds as antifoulants in a process for the thermal cracking of tars to olefins. EP-A-0156614 describes the use of HDD in treating a heavy hydrocarbon oil feed. EP-A-0576982 describes addition of HDD to heavy hydrocarbon oil to prevent coke deposition during cracking. SUMMARY OF THE INVENTION The present invention accordingly has an object to provide an antifoulant for petrochemical processes which can eliminate the drawbacks of the conventional antifoulants for petrochemical processes, can be handled easily, is inexpensive, has no adverse effect on the process, shows excellent effect to prevent the formation of fouling, and enables continuous operation of a plant for a long time with good stability. The present inventors conducted extensive studies to develop an antifoulant for petrochemical processes having the advantageous properties described above. As the result of the studies, it was discovered that the object can be achieved by an antifoulant comprising a hydrogen-donating hydroaromatic compound. The present invention is completed on the basis of the discovery. Thus, the present invention provides an antifoulant for petrochemical processes comprising a hydrogen-donating hydro-aromatic compound. The present invention also provides a process for preventing formation of fouling in a petrochemical plant comprising adding the antifoulant for petrochemical processes described above to a process fluid supplied to petrochemical processes in which fouling is formed. Other and further objects, features and advantages of the invention will appear more fully in the following description. DETAILED DESCRIPTION OF THE INVENTION The present invention is described in detail in the following. As described above, the formation of fouling is caused by oxidation of unsaturated hydrocarbons, such as olefins and diolefins, in a process fluid by radical chain reactions. The hydrogen-donating hydroaromatic compound used as the antifoulant of the present invention has the function of stopping the chain reactions by donating proton to the radical generated in the oxidation and effectively preventing the formation of fouling. Examples of the hydrogen-donating hydroaromatic compound include tetralin, 9,10-dihydrophenanthrene, 1,2,3,4,5,6,7,8-octahydro-phenanthrene, and hydrogenated terphenyl. The compound may be used singly or as a combination of two or more compounds. In the antifoulant of the present invention, conventional antifoulants, such as antioxidants like amine antioxidants and phenol antioxidants, polymerization inhibitors like oxime inhibitors and nitroso inhibitors, metal deactivating agents, and various kinds of dispersant, may be used in addition to the hydroaromatic hydrocarbon according to desire. The dispersant disperses organic sludge and inorganic sludge into the process fluid and prevents adherence of deposit to the surface of heat transfer or the surface of pipings. Examples of the dispersant include: (1) a mixture of a polyalkyl (meth)acrylate having molecular weight of about 1000 to 10000 and a polyethylene polyamine naphthenic acid amide represented by the following general formula: wherein R 1 indicates a hydrocarbon group having 10 to 15 carbon atoms, n indicates an integer of 1 to 5, preferably 1 to 3, and m indicates an integer of 1 to 10, preferably 1 to 3, in a ratio by weight of the respective components in the range of 90 : 10 to 10 : 90; (2) a derivative of succinimide represented by one of the following general formulae: wherein R 2 indicates a polybutene group having a molecular weight of 400 to 3000, R 3 indicates an alkylene group having 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms, R 4 and R 5 indicate each hydrogen atom or an alkyl group having 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms, and p indicates an integer of 1 to 10; (3) a derivative of thiophosphoric acid ester represented by the following general formula; wherein R 6 is a polybutene group having a molecular weight of 500 to 2000, or an ethylene oxide adduct thereof; and (4) a copolymer of styrene and maleic acid ester having a molecular weight of 10,000 to 1,000,000 and represented by the following general formula: wherein R 7 and R 8 indicate each a linear or branched alkyl or alkenyl group having 12 to 18 carbon atoms and q and r indicate numbers showing a ratio by mole of the two kinds of unit (q : r) in the range of 1 : 9 to 9 : 1. The dispersant may be used in combination of two or more kinds according to desire. Examples of the polyalkyl (meth)acrylate used in the dispersant (1) described above include homopolymer of an alkyl (meth)acrylate in which the alkyl group has 5 to 18 carbon atoms, copolymers obtained by copolymerization of two or more kinds of said alkyl (meth)acrylate, and copolymers obtained by copolymerization of one or more kinds of said alkyl (meth)acrylate with one or more kinds of unsaturated monomer having an ethylenically unsaturated bond, such as N-vinyl-2-pyrrolidone and diethylaminoethyl (meth)acrylate. When used as an antifoulant for petrochemical processes the HDD compound is added in an amount which is in the range of 0.5 to 200 mg/liter based on the amount of process fluid. When used in combination with dispersant the amounts of components are not particularly limited but are suitable selected. The process fluid to which the antifoulant of the present invention is applied is not particularly limited. The antifoulant of the present invention can be applied to any kind of oil for treatment in which fouling is formed in treatments in petrochemical processes. It is preferably applied to process oils treated in a preliminary heat exchanger or a reboiler in a distillation tower, such as a depropanizer, a de-ethanizer, a debutanizer, or a condensate stripper, in an ethylene plant. An example of the preferable method of application of the antifoulant of the present invention is described in the following. The hydrogen-donating hydroaromatic compound and other components, such as other antifoulants and additional components, which are used additionally according to necessity are dissolved in a suitable solvent to prepare a solution having a concentration of about 0.5 to 60 % by weight. The solution thus prepared is added continuously to an apparatus in which fouling is formed in the petrochemical process, such as a heat exchanger, a reboiler or pipings or added to the tank of a material oil in all the amount at one time. The amount of the antifoulant of the present invention added to the process fluid is in the range of 0.5 to 200 mg/liter, based on the amount of the process fluid. Because the antifoulant of the present invention has the excellent property to prevent the formation of fouling, continuous operation for a long time, such as for two to three years, is made possible with good stability, in contrast to continuous operation generally practiced for only 3 months when a conventional antifoulant is used. As the result, energy saving and reduction of maintenance cost can be expected and, furthermore, risk accompanied with emergency stopping of the plant can be avoided. To summarize the advantages obtained by the invention, the antifoulant for petrochemical processes can be handled easily, is inexpensive, has no adverse effect on the process, shows excellent effect to prevent formation of fouling, enables continuous operation of a plant for a long time with good stability and brings energy saving and reduction of maintenance cost. The invention will be understood more readily with reference to the following examples; however, these examples are intended to illustrate the invention and are not to be construed to limit the scope of the invention. Examples 1 to 6 and Comparative Examples 1 to 4 Agents of the kinds and the amounts shown in Table 1 were added to a depropanizer bottom fluid taken from a plant in operation. The mixture was charged to a 200 milliliter autoclave made of SUS 304 and treated with heat at 100°C for 20 hours. Then, the treated fluid is distilled under a reduced pressure and dried to obtain amount of the residue of evaporation (amount of formed polymer). Rate of suppression of the formation of fouling was calculated for evaluation of the anti-fouling property as the ratio of the value obtained above to the corresponding value obtained in the absence of the agent. Results are shown in Table 1. In Table 1, the dispersant is a copolymer of styrene and a maleic acid ester having a molecular weight of 15000 and TBC indicates t-butylcatechol. agent amount of formed polymer (% by wt. of the total fluid) rate of suppression (%) kind amount used (mg/kg) Example 1 tetralin 10 0.030 90 Example 2 tetralin 20 0.026 92 Example 3 tetralin 10 0.006 98 dispersant 10 Example 4 tetralin 20 0.003 99 dispersant 20 Example 5 9,10-dihydrophenanthrene 20 0.004 99 dispersant 20 Example 6 hydrogenated terphenyl 10 0.004 99 dispersant 20 Comparative Example 1 p-nitro-o-cresol 10 0.016 95 Comparative Example 2 p-nitro-o-cresol 20 0.006 98 Comparative Example 3 aniline 5 0.096 70 TBC 5 dispersant 10 Comparative Example 4 aniline 10 0.064 80 TBC 10 dispersant 20 (Note) Amount of the formation of fouling when no agent was added was 0.320 % by weight based on the total amount of the fluid. Comparative Examples 1 and 2 showed good results on the rate of suppression of the formation of fouling. However, p-nitro-o-cresol cannot be used practically because of the problem on handling.

Claims: Use of a hydrogen-donating hydroaromatic compound as an antifoulant for petrochemical processes, wherein the hydrogen-donating hydroaromatic compound is added to a petrochemical process fluid in an amount which is in the range of 0.5 to 200 mg/liter based on the amount of the process fluid. Use of claim 1, wherein the hydrogen-donating hydroaromatic compound is used as an antifoulant in a depropanizer of an ethylene plant. A use as claimed in Claim 1, wherein the hydrogen-donating hydroaromatic compound is a compound selected from the group consisting of tetralin, 9,10-dihydrophenanthrene, 1,2,3,4,5,6,7,8-octahydrophenanthrene and a hydrogenated terphenyl. An antifoulant for petrochemical processes comprising a hydrogen-donating hydroaromatic compound and a dispersant for sludge. An antifoulant for petrochemical processes as claimed in Claim 4, wherein the dispersant for sludge is at least one selected from the group consisting of a mixture of a polyalkyl (meth)acrylate and a polyethylene polyamine naphthenic acid amide, a derivative of succinimide, a derivative of a thiophosphoric acid ester or an ethylene oxide adduct thereof, and a copolymer of styrene and a maleic acid ester. A use of Claim 1 comprising adding the hydrogen-donating hydroaromatic compound to a process fluid supplied to petrochemical processes in which fouling is formed in a petrochemical plant. A use of Claim 6, wherein the hydrogen-containing hydroaromatic compound is added continuously to the process fluid at a position before the apparatus in a petrochemical plant in which apparatus the fouling is formed. A use of Claim 6, wherein the petrochemical plant is an ethylene plant. A use of Claim 6, comprising adding the hydrogen-donating hydroaromatic compound and a dispersant for sludge. A use of Claim 9, wherein the dispersant for sludge is at least one selected from the group consisting of a mixture of a polyalkyl (meth)acrylate and a polyethylene polyamine naphthenic acid amide, a derivative of succinimide, a derivative of a thiophosphoric acid ester or an ethylene oxide adduct thereof, and a copolymer of styrene and a maleic acid ester.

Inventors: IRIE KATSUTOSHI, TANAKA KOICHI, IRIE, KATSUTOSHI, TANAKA, KOICHI, IRIE, KATSUTOSHI, C/O KURITA WATER INDUSTRIES LTD., TANAKA, KOICHI, C/O KURITA WATER INDUSTRIES LTD.
Applicants: KURITA WATER IND LTD, KURITA WATER INDUSTRIES LTD.
Application year: 1994
Main classification: C10G75
IPC codes: C10G9, C10G7